Fitted sheets have been designed in the past in the attempt to overcome a few basic problems involved with securing and tensioning the sheet. The problems include holding the sheet in place on the mattress; holding the sheet tight and wrinkle free across the top face of the mattress and at the same time providing for their easy removal and replacement.
The most popular design and the one in use over much of the world is the elastic corner design. This design provides for the easy application and removal of the sheet but does not anchor the sheet securely; they often come loose and are never held completely tight across the face of the mattress.